Defrost method and means for refrigerated cabinets



Sept. 8, 1964 s. BECKWITH 3,147,602

DEFROST METHOD AND MEANS FOR REFRIGERATED CABINETS Filed July 31, 1961 2Sheets-Sheet l OOOOOOO OOOOOOO OOOOOOO FIG, 5

mmvrop. Sterlmg Beckwzih @101 BY M,%.@ MM Fm. 3 M7 Q1295 S. BECKWITHSept. 8, 1964 DEFROST METHOD AND MEANS FOR REFRIGERATED CABINETS FiledJuly 51, 1961 2 Sheets-Sheet 2 lllll I WUNMQMPMG WMM l I l United StatesPatent "ice 3,147,602 DEFROST METHOD AND MEANS FOR REFRIGERATED CABINETSSterling Beclrwith, Libertyville Township, Lake County,

Ill assignor, by mesne assignments, to Dual Jet Refrigeration Company, acorporation of Illinois Filed July 31, 1961, Ser. No. 128,235 16 Claims.(Cl. 62278) This invention relates to a refrigeration system and moreparticularly to a refrigeration system which requires occasional defrostfor the removal of frost collected on the surfaces of the evaporatorplates.

The invention will be described with reference to the maintenance of arefrigerated state Within a space that is enclosed except for an openside which remains open to the atmosphere for observation of theproducts maintained within the refrigerated space and for access intothe interior thereof to remove refrigerated products or for replacementof products for refrigeration and display. It will be understood thatthe concepts of this invention of refrigeration and defrost will haveapplication to refrigeration systems employed for uses other than in arefrigerated display cabinet of the type described.

In the copending application of Hagen et al., Ser. No. 54,077, filedSeptember 6, 1960, and entitled Refrigerated Display Case, descriptionis made of a refrigerated display cabinet having a storage space with anopen side. Loss of heat from the storage space through the open side issubstantially obviated by the use of a curtain of air passedcontinuously across the space from one edge to an opposite edge therebyto blanket the entire opening.

The air curtain is adapted to be formed of adjacent panels of air withthe inner panel being a refrigerated panel while the outer panel orpanels correspond more closely to the ambient temperature. For mostefficient operation, it has been found desirable to recirculate at leastthe inner panel of cold air to conserve on the investment inrefrigeration and to maintain the space in the desired refrigeratedstate.

In the aforementioned copending application, illustration is made of anarrangement which makes use of an inner cold air panel and an outerpanel both of which are recirculated through separate systems in thecabinet whereby the outer panel acquires a temperature intermediate thecold air panel and the ambient temperature to function as a guard panelwhich minimizes heat loss while at the same time enhancing laminar flow.Also disclosed in the aforementioned copending application is anarrangement wherein the curtain is formed of three recirculating panelsarranged in side-by-side relationship further to increase the efiiciencyof operation from the standpoint of laminar flow characteristics andheat loss from the conditioned space.

Description is made of an arrangement wherein the nozzles, from whichthe air panels issue, extend across the bottom edge of the opening todirect the air panels upwardly across the open space towards inletswhich extend across the top side of the opening. Description is alsomade of a preferred arrangement wherein the nozzles are located acrossthe upper edge of the opening for issuing the air panels downwardlyacross the opening to inlets arranged across the bottom side. It will beunderstood that the air nozzles can be located across one of the lateraledges of the opening for directing the air panels across the openingtowards inlets in the opposite edge. Because of the more desirableeffect of gravity on the high density cold air, it is preferred to flowthe air curtain downwardly from nozzles across the top to inlets acrossthe bottom.

Refrigeration of the cold air panel is achieved by the use of arefrigeration system wherein a refrigerant liquid 3,147,562 PatentedSept. 8, 1954 is circulated through an evaporator located within thecold air passage beyond the inlet but before the outlet and throughwhich the cold air stream must pass in heat exchange relationship. Sincethe air is gradually reduced in temperature as it passes progressivelyfrom the ambient atmosphere into the outer guard panels and from theouter guard panels into the inner cold air panel to form a part thereofbefore passing into the refrigerated space, the relative humidity of theair correspondingly increases to a point where it becomes substantiallysaturated with moisture by the time that it becomes part of the cold airpanel. Such moisture tends to separate out and collect on the coldsurfaces impacted by the cold air stream, especially when such surfacesconstitute a cold surface such as the evaporator plate or coils. Asaresult, moisture collects as frost on the evaporator plates andparticularly on the ingoing side.

Excessive frost formation requires termination of the cold air fiowuntil the surfaces of the evaporator plates can be defrosted. In orderproperly to maintain the refrigerated state, it is desirable to minimizethe number of times and the length of time that the flow of the cold airstream is shut off and for this purpose it is desirable either tominimize the amount of frost built up on the surfaces of the evaporatorplates and/or else to maximize the rate at which such frost can beremoved.

Thus it is an object of this invention to produce a method and means forreducing the built-up frost on the surfaces of refrigeration coilslocated within the path of an air stream for the refrigeration thereof.

Another object of this invention is to provide a method and means forrapid defrost thereby to minimize the length of time required to effectfrost removal and replacement of the refrigeration coils back into therefrigeration cycle. 7

A further object is to provide a display cabinet having a refrigeratedspace which is enclosed except for an open side across which one or morestreams of air are projected as an air curtain from one side to theother across the open space with the inner panel of the curtain being arefrigerated cold air panel which is continuousl recirculated and whichis maintained in a refrigerated state by a refrigeration systemincluding an evaporator plate in the path of the cold air stream passagein heat exchange relationship therewith and which embodies means forminimizing the concentration of frost built up on the surfaces of theevaporator plates thereby to lengthen the time span between the defrostcycles and/or increase the rate of frost removal thereby to minimize thelength of time that the cold air stream is taken out of circulation.

These and other objects and advantages of this invention willhereinafter appear and for purposes of illustration, but not oflimitation, embodiments of the invention are shown in the accompanyingdrawings, in which- FIG. 1 is a schematic sectional elevational view ofa refrigerated display cabinet embodying the features of this invention;

FIG. 2 is a schematic sectional elevational View similar to that of FIG.1 showing a modification in the cabinet construction;

FIG. 3 is a sectional elevational view similar to those of FIGS. 1 and 2showing a further modification in the cabinet construction;

' FIG. 4 is a flow diagram of the refrigeration system embodying thefeatures of this invention; and

FIG. 5 is a schematic sectional elevational view of a portion of thecabinet embodying a further feature of this invention.

The concepts of this invention are found to be most eifective when usedin combination with a refrigerated display cabinet of the type describedwherein an air curtain is used to protect an open side of an otherwiseenclosed refrigerated space to maintain the desired state ofrefrigeration therein. Thus the invention will be described withreference to the combination of the refrigeration system and an openrefrigerated display cabinet. However, it will be understood that theconcepts of the invention will have application to other refrigerationsystems wherein rapid defrost finds beneficial use.

Referring now to the drawings for a description of the refrigerateddisplay cabinet and its method of operation, the cabinet is constructedwith an outer housing wall including a top wall 12, a back wall 14, abottom wall 16, vertical side walls 18, and a front wall 20, the latterbeing provided with an access opening 22. The housing rests upon asuitable base 24.

Spaced inwardly from the housing walls in substantially parallelrelationship is an inner wall including top, back, bottom, side andfront walls 26, 28, 30, 31 and 32, respectively, which define theinterior of a storage space 34. The space between the inner walls andthe housing walls is divided by a partitioning wall 36 into twoseparated passages 38 and 40 which extend substantially continuouslyabout the storage space from outlets 54 and 56 across the bottom side ofthe opening 22 to inlets 62 and 64 across the top side of the opening22.

Located within the inner passage 40 are evaporator coils 42 throughwhich a suitable refrigerant is circulated for indirect heat exchange tocool air passing through the cold air passage 40 into contact with theevaporator coils. Located upstream between the evaporator coils 42 andthe inlet 62 is an air circulating means, such as a fan or blower 44,for causing the stream of air to flow through the passage 40 from theinlet 62 to the outlet 54 and from the outlet 54 to the inlet 62 acrossthe open space 22 to form the inner cold air panel 58 of the aircurtain.

Similarly located within the outer passage 38 is another air circulatingmeans, such as a fan or blower 46, for causing air to flow from theinlet 64 through the channel to the outlet 56 and from the outlet 56 tothe inlet 64 across the open space 22 to form the outer panel 60 whichflows in substantially parallel relationship with the inner cold airpanel 58 to form the air curtain.

The outlet 54 of the cold air passage 40 is in the form of a vanednozzle 55, such as a honeycomb section, which extends continuouslyacross the bottom side of the access opening 22 in the front wall of therefrigerated display case. Similarly the outlet 56 for the outer guardair passage 38 is in the form of a nozzle 57 of a vaned or honeycombsection which also extends substantially continuously across the bottomside of the access opening in parallel side-by-side relationship withthe nozzle 55.

The streams of air issuing from the outlets 54 and 56 form continuousinner and outer air panels 58 and 60 which extend across the accessopening 22 from the outlets 54 and 56 to the inlets 62 and 64. Thenozzle 55 is positioned to direct the inner cold air panel 58 to theinlet 62 in communication with the cold air passage 40 while the nozzle56 is positioned to direct the outer guard air panel 68 to the inlet 64in communication with passage 38. Both of the inlets can be providedwith screening members 66 and 68 to obviate the entrance of foreignmatter, insects and the like into the passages.

From the foregoing description it will be apparent that the deviceprovides a panel of cold air 58 adjacent to the interior of the storagespace and a panel of warmer air 68 which will be intermediate thetemperature of the cold air panel and the temperature of the ambientair. Thus the guard panel 60 is interposed between the inner panel ofcold air and the ambient air thereby to guard the cold air from the heatof the atmosphere and whereby air entrained from the guard panel intothe cold air panel will be found to be at considerably lower temperaturethan the air from the atmosphere which otherwise would be the componentadmixed therewith. To minimize heat loss into the cold air recirculatedthrough the passage 48, it is desirable, though not essential, that thepartitioning wall 36 and the outer wall 14 be provided with suitableinsulation, designated by the numeral 74.

By way of still further modification, instead of making use of a singleguard jet, additional guard jets may be provided whereby the air panelsextending across the access opening will correspond to the number ofsuch jets. In the modification illustrated in FIG. 3 one additionalguard jet 102 is employed to provide three parallel streams of air 58,60 and 102 extending across the access opening. It will be understoodthat more than one additional. jet may be provided. Such additional jetswill operate further to reduce the temperature diiferential between theair panels so that the guard jet adjacent the inner cold air panel willbe at a temperature still closer to the temperature of the cold airstream such that the entrainment of air from one panel to the other willhave lesser effect on the temperature thereof.

The modifications illustrated in FIGS. 2 and 3 will be the preferredmodifications wherein the air streams are circulated through thepassages from inlets at the bottom to outlets at the top of the accessopening and downwardly from the outlets across the top of the accessopening to inlets across the bottom of the access opening.

In FIG. 1, the evaporator coils 42 of the refrigeration system arelocated in the vertically disposed portion of the cold air passagerearwardly of the enclosed refrigerated space. In the preferred practiceof the invention, illustrated in FIGS. 2 and 3, wherein the air streamsare recirculated through the passages for downward flow across theaccess opening 22 from outlets across the top to inlets across thebottom, the evaporator coils 42 of the refrigeration system are locatedin the passages extending horizontally across the bottom sides of thecabinet. In either event, the evaporator coils are provided with a drainpan 188 for collecting the moisture released when the frost is meltedfrom the surface of the evaporator coils during the defrost cycle andeach drain pan is provided with a connecting hose 101 for the drainageof moisture collected in the pans.

Having described the construction and operation of the refrigerateddisplay cabinet, description will now be made of the concepts of thisinvention in a system which embodies means for rapid defrost.

Referring now to FIG. 4 of the drawings, the evaporator located in thecold air passage is identified by the numeral 42 and the evaporator(when employed) in the guard air passage is identified by the numeral 48and the drain pan is illustrated by the numeral 100. The other elementsconventionally employed in a refrigeration system include a compressor104, a condenser 106, and a receiver 108 whereby liquid refrigerant 110is passed from the receiver through line 112 through a drier 114 andfrom the drier through line 116 through a heat exchanger 118 throughline 120 to the solenoid valves 122 which control passage of therefrigerant liquid into the coils of the evaporator 42 or 42 and 48. Therefrigerant vapors from the evaporator coils pass through line 124through the heat exchanger 118 and defrost receiver 126 to thecompressor 104 where the vapors are recompressed and then advancedthrough line 128 to the condenser 106 wherein the compressed refrigerantvapors are condensed to the liquid state for return through line 130 tothe receiver 108.

Occasionally it is necessary to shut off the refrigeration cycle toenable removal of frost collected on the surfaces of the evaporatorcoils. Various techniques have been employed for defrosting theevaporator coils in a refrigeration system. One such technique to whichthis invention is addressed is often referred to as hot gas defrostwherein the refrigerant vapors exhausted from the compressor and heatedup by the work performed in compression are recirculated through theevaporator coils for condensation, to melt the frost collected on thesurfaces thereof. Sometimes the heat introduced into the exhaust gasesby the compressor is supplemented by external heat supplied by heatexchange relationship with the hot liquids advanced through the line 132to the evaporator coils.

The defrost cycle using the conventional hot gas defrost requires such alength of time as to enable change in the temperature conditionsexisting within the refrigerated space. It has been found, in accordancewith an important concept of this invention, that the defrost cycle canbe markedly shortened by modification of the hot gas defrost systemgreatly to increase the volume of hot gases which are circulated throughthe evaporator coils.

For this purpose, there is provided an auxiliary supply of refrigerantliquid in communication with the discharge line 130 or 132 from thecompressor whereby the pressure conditions existing when the hot gasesfrom the compressor are recirculated to the refrigeration coils duringthe hot gas defrost cycle draw the refrigerant liquid from the auxiliarysupply into the return line 132. Auxiliary heaters 134 are provided forheat exchange with the line 132 to reduce the refrigerant liquid to thegaseous state thereby materially to increase the volumetric heat flow ofgases to the evaporator coils. The quantity increase of heat flow of hotgases to the evaporator operates materially to reduce the defrost cycleto a matter of a few minutes compared to at least three to four times aslong for conventional hot gas defrost systems.

In the illustrated modification, the auxiliary liquid refrigerant iscollected in a pan 136 located within the receiver 108 and into whichthe end of the line 130 from the condenser extends so that the condensedrefrigerant liquid is first deposited into the pan and the overflowfalls from the pan into the receiver. Thus the pan is immediatelyrefilled with refrigerant liquid during the normal refrigeration cycleand it can be dimensioned to hold refrigerant liquid in an amountdesired to supply the additional volume of gases for defrost. Usually,an auxiliary supply of from to 12 pounds will be sufficient. instead ofcollecting the liquid in a pan forming a part of the receiver, theauxiliary liquid can be supplied in a container separate and apart fromthe receiver but which communicates with the line 132 through which thehot exhaust gases are advanced to the refrigeration coils for defrost.

In operation, the defrost cycle is initiated by an electrical signalwhich may be responsive to the frost buildup on the evaporator coils orto a temperature differential control or to a timer or otherconventional means for signaling the termination of a refrigerationcycle and the initiation of the defrost cycle. In sequence with thesignal, the liquid solenoid valve 122 is closed to shut off How ofrefrigerant liquid in the evaporator coils. After a short period forvaporization of the refrigerant liquid remaining in the coils, thesuction solenoid valve 137 is closed and simultaneously the hot gassolenoid valve 138 is opened for circulation of the hot gases exhaustedfrom the compressor through line 132 to the inlet side of the evaporator42.

In conjunction with the opening of the hot gas solenoid 138, a dischargepressure drop occurs which draws or otherwise forces the small quantityof auxiliary refrigerant liquid from the auxiliary supply pan 136 intothe discharge line 130 and the hot gas line 132. As the auxiliary liquidis advanced through the air cooled condenser 106 and the hot gas line132 provided with the heating means 134, such as an electricalresistance heater or other heating means, the liquid boils and absorbsheat whereby the auxiliary refrigerant liquid is converted into a largevolume of heated gases or vapor. The total heat of the hot gasesexhausted from the compressor and the hot gases of the converted liquidis advanced through the line 132 to the evaporator since evaporation isat a lower temperature and pressure. The heat from the total volume ofhot gases is absorbed by the evaporator coils to cause rapid melting ofthe frost collected on the surfaces thereof.

It is preferred that the heating means 134 be a low energy source suchthat it will not evaporate the rapid flow of liquid from the supply pan136 unless it has, over a period of time, which is a substantial portionof the time between defrosts, stored thermal energy in the mass of metalwhich constitutes the hot gas line 132. Under such circumstances therewill be a relationship between the volumetric capacity of supply pan 136and the mass of hot gas line 132. Also line 132 should have adequateinside surface area to transfer its heat rapidly to the liquid flowingfrom pan 132.

The hot gases are, in turn, condensed for reconversion into liquid formwhich accumulates in the evaporator suction line side of the evaporator.A capillary tube 140 which bypasses the suction solenoid 137 operates todischarge the accumulated liquid into the suction line 124 for return tothe compressor and recycling.

A further concept of this invention resides in the construction andarrangement of the evaporator whereby the build up of frost is spreadover a larger area of the surface of the refrigeration coils thereby toextend the length of time between the defrost cycles. For this purpose,as illustrated in FIG. 5, the passage 40 leading to the inlet end of theevaporator is dimensioned to have a crosssection greater than thecross-section of the evaporator with the walls 142 of the passageconverging to engage the evaporator walls intermediate the inlet andoutlet ends so that a fractional portion of the air stream will impactthe evaporator at the inlet end while the remaining portions will impactthe evaporator for passage therethrough along the side walls beyond theinlet thereby materially to increase the surface area of the evaporatoron which moisture can condense to form frost.

' Such distribution of frost over a greater surface area of theevaporator coils has been found proportionately to increase the amountof time that the evaporator can remain in the cooling cycle beforeinitiation of the defrost cycle and it also inversely reduces the amountof time required to defrost the coils since there will be a lesser buildup of frost per unit area .of surface and greater surface area isavailable for heat transfer from the hot gases advanced through thecoils during the defrost cycle.

It will be apparent from the foregoing that I have provided a method andmeans for materially shortening the defrost cycle thereby to minimizethe length of time that the refrigeration system is taken out ofoperation. It will be apparent that this material reduction in the timerequired to defrost the evaporator coils will operate beneficially tomaintain the refrigerated state within the storage space of arefrigerated display cabinet of the type to which this invention isprincipally addressed thereby materially to enhance the utility of therefrigerated display cabinet for the display and storage of refrigeratedproducts.

It will be understood that changes may be made in the details ofconstruction, arrangement and operation Without departing from thespirit of the invention, especially as defined in the following claims.

I claim:

1. In a refrigeration system having an evaporator, a compressor, acondenser and a receiver wherein refrigerant liquid is circulated fromthe receiver to the evaporator and wherein the refrigerant vapors arecirculated from the evaporator to the compressor for recompression andfrom the compressor to the condenser where the compressed vapors arecondensed for return to the receiver, a defrost system comprising apassage communicating the discharge from the compressor with theevaporator for circulation of the hot vapors exhausted from thecompressor to the evaporator, an auxiliary supply of refrigerant liquidin communication with the passage whereby refrigerent liquid is drawnfrom the auxiliary supply into said passage responsive to thecirculation of the hot vapors exhausted from the compressor through thepassage to the evaporator, and heating means in heat exchangerelationship with the auxiliary liquid advanced to the passage toconvert said refrigerant liquid to the vapor state and for heating samewhereby the total volume of hot vapors advanced to the evaporator fordefrost comprises the hot vapors exhausted from the compressor plus thelarge volume from the so converted auxiliary refrigerant liquid to causerapid defrost of the evaporator.

2. A refrigeration system as claimed in claim 1 which includes ashut-off valve for stopping the flow of refrigerant liquid from thereceiver to the evaporator prior to the circulation of the hot vaporsfrom the discharge and the auxiliary refrigerant liquid to theevaporator.

3. A refrigeration system as claimed in claim 2 in which the passagecommunicating the discharge from the compressor with the evaporatorcommunicates with the evaporator beyond the shut-off valve and whichincludes another shut-oti valve in the passage between the dischargefrom the compressor and the evaporator.

4. A refrigeration system as claimed in claim 1 in which the heatingmeans comprises a heater in heat exchange relationship With the passagebetween the discharge from the compressor and the evaporator.

5. A refrigeration system as claimed in claim 1 which includes acontainer within the receiver of smaller capacity than the receiver anda passage having one end in communication with the condenser and theother end terminating in the container for the delivery of refrigerantliquid from the condenser to the container to fill the container beforeoverflow from the container into the receiver.

6. A refrigeration system as claimed in claim 1 in which the auxiliarysupply of refrigerant liquid comprises a container Within the receiver.

7. In a refrigerated display cabinet having a refrigerated spaceprovided with an access opening communicating the otherwise enclosedspace with the outside atmosphere, means for projecting a continuouscurtain of refrigerated air across said access opening from an outletacross one side of said opening to an inlet across the opposite side ofsaid opening, a passage in said cabinet communicating the inlet with theoutlet for recirculating the air from the inlet to the outlet, andevaporator located within said passage and a refrigeration system incommunication with said evaporator including a compressor, a condenserand a receiver wherein refrigerant liquid is circulated from thereceiver to the evaporator and wherein the refrigerant vapors arecirculated from the evaporator to the compressor for recompression andfrom the compressor to the condenser where the compressed vapors arecondensed for return to the receiver, a defrost system comprising apassage communicating the discharge from the compressor with theevaporator for circulation of the hot vapors exhausted from thecompressor to the evaporator, an auxiliary supply of refrigerant liquid,in communication with the passage whereby refrigerant liquid is drawnfrom the auxiliary supply into said passage responsive to thecirculation of the hot vapors exhausted from the compressor through thepassage to the evaporator, and heating means in heat exchangerelationship with the auxiliary liquid advanced to the passage toconvert said refrigerant liquid to the vapor state and for heating samewhereby the total volume of hot vapors advanced to the evaporator fordefrost comprises the hot vapors exhausted from the compressor plus thelarge volume from the converted auxiliary refrigerant liquid to causerapid defrost of the evaporator.

8. A refrigerated display cabinet as claimed in claim 7, which includesa shut-ofi valve for stopping the flow of refrigerant liquid from thereceiver to the evaporator prior to the circulation of the hot vaporsfrom the discharge and the auxiliary refrigerant liquid to theevaporator.

9. A refrigerated display cabinet as claimed in claim 8 in which thepassage communicating the discharge from the compressor with theevaporator communicates with the evaporator beyond the shut-off valveand which .includes another shut-off valve in the passage between thedischarge from the compressor and the evaporator.

10. A refrigerated display cabinet as claimed in claim 7 in which theheating means comprises a heater in heat exchange relationship with thepassage between the discharge from the compressor and the evaporator.

11. A refrigerated display cabinet as claimed in claim 7 which includesa container within the receiver of smaller capacity than the receiverand a passage having one end in communication with the condenser and theother end terminating in the container for the delivery of refrigerantliquid from the condenser to the container to fill the container beforeoverflow from the container into the rece ver.

12. A refrigerated display cabinet as claimed in claim 7 in which theauxiliary supply of refrigerant liquid comprises a container within thereceiver.

13. A refrigerated display cabinet as claimed in claim 7 which includesa drain pan underlying the evaporator for drainage of the liquiddefrost.

14. A refrigerated display cabinet as claimed in claim 7 which includesmeans for terminating the flow of air through said passage during thedefrost cycle.

15. A refrigerated display cabinet as claimed in claim 7 in which thepassage about the ingoing side of the evaporator is of larger dimensionthan the evaporator to provide an access space about the leading endportion of the evaporator whereby the circulating air may enter theevaporator for passage theret-hroug-h about the side wall portions inaddition to the leading end portion.

16. A refrigerated display cabinet as claimed in claim 15' in which thepassage is defined by walls which are spaced from the outer surfaces ofthe evaporator in the leading end portion and converged to engage theevaporator mtermediate its ends.

References Cited in the file of this patent UNITED STATES PATENTS

1. IN A REFRIGERATION SYSTEM HAVING AN EVAPORATOR, A COMPRESSOR, ACONDENSER AND A RECEIVER WHEREIN REFRIGERANT LIQUID IS CIRCULATED FROMTHE RECEIVER TO THE EVAPORATOR AND WHEREIN THE REFRIGERANT VAPORS ARECIRCULATED FROM THE EVAPORATOR TO THE COMPRESSOR FOR RECOMPRESSION ANDFROM THE COMPRESSOR TO THE CONDENSER WHERE THE COMPRESSED VAPORS ARECONDENSED FOR RETURN TO THE RECEIVER, A DEFROST SYSTEM COMPRISING APASSAGE COMMUNICATING THE DISCHARGE FROM THE COMPRESSOR WITH THEEVAPORATOR FOR CIRCULATION OF THE HOT VAPORS EXHAUSTED FROM THECOMPRESSOR TO THE EVAPORATOR, AN AUXILIARY SUPPLY OF REFRIGERANT LIQUIDIN COMMUNICATION WITH THE PASSAGE WHEREBY REFRIGERENT LIQUID IS DRAWNFROM THE AUXILIARY SUPPLY INTO SAID PASSAGE RESPONSIVE TO THECIRCULATION OF THE HOT VAPORS EXHAUSTED FROM THE COMPRESSOR THROUGH THEPASSAGE TO THE EVAPORATOR, AND HEATING MEANS IN HEAT EXCHANGERELATIONSHIP WITH THE AUXILIARY LIQUID ADVANCED TO THE PASSAGE TOCONVERT SAID REFRIGERANT LIQUID TO THE VAPOR STATE AND FOR HEATING SAMEWHEREBY THE TOTAL VOLUME OF HOT VAPORS ADVANCED TO THE EVAPORATOR FORDEFROST COMPRISES THE HOT VAPORS EXHAUSTED FROM THE COMPRESSOR PLUS THELARGE VOLUME FROM THE SO CONVERTED AUXILIARY REFRIGERANT LIQUID TO CAUSERAPID DEFROST OF THE EVAPORATOR.